I had such a hard time with this issue with my 4yr old, but I am happy to report he's finally #2 potty trained..yay! It took A LOT of patience and trial and error to find what worked.

At first, we did the lollipop and a TON of praise if he pooped in the potty. Often he did not want to stop playing with electronic toys to use the toilet. He pooped in his pants and would sit in the dirty underwear while playing with his toys. That got old real fast. So, we resorted to making him wash his dirty underwear in the toilet. I did not make a big deal out of the act either. "Take off the dirty pants and wash them in the toilet." He was not happy with having to do this. I did consult with a child psychologist who specialized in autism and she confirmed that this was a frequently used method.

About that same time, I also introduced the 'poop on potty' chart. For each successful deposit, he'd get a lollipop (instant gratification) and then stamp a chart to work toward a bigger prize after 5 times. I also payed close attention to find some predictable pattern in his bowel movements to encourage him on the right path.

When I increased the number of 'stamps' needed for the prize, I put the item in a 'mystery bag' that sits on top of the fridge. I often find the element of suspense is greater than/equal to the joy of earning the item for him.

My son still has a fear of using other toilets than home for bowel movements. With our ABA therapy we've made a social story about 'going poop on the potty in other places'. Those self flushing toilets scare the **** out of me sometimes, so when I see one I prepare my son by saying the toilet will flush by itself. I also let him flush the toilet when we enter the stall to give him some sense of control and to desensitize him to the sound a little. Only recently has he started using toilets in other places than home and often they are toilets similar in style to what's at home (ie - a relative's house or doctor's office). When he does poop in another place, there is a HUGE celebration and he knows that he still earns the reward even if we aren't home.

Good luck!

My NT DD has bowel problems. I use to think it was out of pure stubbornness. Well, now I know it is due to an actual medical problem called Encopresis which is caused by chronic constipation. They get constipated and it hurts to go. So, they hold it until they can't hold it anymore. They also begin to associate sitting on the toilet with pain as it becomes very painful for them to have a bowel movement. Eventually, they become impacted and they can't have a normal bowel movement and even lose the sensation of urge when the need to go. My DD was diagnosed and we use Mirlax as well as a very high fiber diet. I give her foods high in fiber as well as a chewable fiber supplement. I see a huge difference in her stools. She still has accidents but she is now able to feel when she has to go, though it is usually too late to make it to the toilet. It will take some time for her bowel nerves and muscles to return to normal but we are on our way to recovery. She will likely always need a high fiber diet. When she was a baby, we had to give her prunes on a daily basis or she would get so constipated. Looking back, it should have been much easier to figure out.

I have read that Encopresis is a common issue with kids with ASD.

From what I know now, I would highly suggest that parents of kids who are trained for urination but not bowels and are at least 4-5 years of age, especially if you know your kid has had a history of constipation, to talk to their child's medical provider. We did a simple abdominal x-ray and had our answer. At that point, my DD was 6 and we'd been trying to potty train for years! I was at my wits end with her and thought she was being difficult. Little did know that, all along, she had no control.

As our son matured, we finally found through testing that he had "mega-colon" which means that the bowel was enlarged and held too much. That made it almost impossible to dispel. Unfortunately, we didn't know this when he was small and we were trying to potty-train him (age 2-5). I took him to the doctor then, and they said that nothing was wrong. He seemed fearful of sitting on the regular toilet (like afraid it would swallow him), so he had a potty-chair. I'm afraid he sat on that quite a bit with no results, but like my husband has said, "If you hadn't stuck with it, he might not ever have been potty-trained." Luckily, finally we made it. He still takes colace to help with the situation after all these years. I pray that the "light-bulb" will come on in your child's mind about it all soon! When they don't quite understand the reasoning behind it all (and sometimes don't experience the "urge")...it makes it VERY difficult, I know! I feel for you! Hang in there!

I just started training with my girl aka we are on day number 2, but I let her watch you tube videos of kids going to the potty on the potty chair and we talk about what they are doing. It worked for #1, but we will see about #2.

I assume you are having trouble with this? We aren't completely out of the woods on this one either, but our ABA program person keeps addressing it in different ways and accidents are getting less. We do rewards which change according to what might motivate him at the moment. Then there is the sticker chart which waxes and wanes in his interest. He just asked for the "no accident" chart to go back up and he gets a sticker for each day with no accidents and so many stickers (a week) means an extra special reward. Then it starts over.
We also still take him to the bathroom on a schedule because he won't tell us when he needs to go and is fine with going in his pants. He is 6 and it doesn't bother him to have a bowel movement in his pants and sit in it. He sometimes fights not to go to the bathroom, but we again bribe to do anything we can to stick to a schedule otherwise, usually when he gets his way and doesn't sit down is when not five minutes later we have an accident on our hands and are in there cleaning him up anyway.
However, all that to say, it has gotten much better in 3 years. He has an accident maybe once or twice a week still, but compared to every bowel movement every day is a huge improvement. Hang in there!